Not normally, driving below the posted maximum speed limit would not, in and of itself.
It might -- and, given the soft nature of upper limits, it might even without driving below the posted maximum -- in the presence of other traffic, depending on the road (what will impede traffic on a single-lane road is different than what will impede traffic on a multilane road) and particular traffic conditions.
Could/would they drive well below the speed limit without legal problem when no traffic is around? I imagine they could, but I'm less interested in that (but understand my question was ambiguous).
Could you, in the same situation, also get a ticket for following the traffic—i.e. breaking the speed limit?
Some speed limits in California are soft (it depends which of the provisions allowing speed limits they are adopted under, or whether they are the default limits.)
It is legally possible for traffic to exceed the speed limit where those limits are soft without necessarily being illegal, unreasonable, or safe.
It may, in some circumstances, therefore, possible to impede reasonable flow of traffic while driving at the speed limit in those cases, thus breaking the law.
> Could you, in the same situation, also get a ticket for following the traffic—i.e. breaking the speed limit?
Yes, but if the circumstances were such that someone could be impeding traffic at the speed limit, it would also necessarily be true that it would possible for you to exceed the speed limit and not be breaking the law. But the burden of proof would be on you to show that the driving was safe.
Wouldn't driving below the posted speed limit when there are no hazardous conditions fall under "as to impede or block the normal and reasonable movement of traffic"?